1. Field of the Invention
The present invention relates to apparatus for constructing cast in place tubular piles and to a method of constructing such piles by the same apparatus.
2. Description of the Prior Art
An application filed earlier by V. Fyoklin et al. discloses an apparatus including a drill column, a hollow soil displacing tool having a helical ribbon surface and a tip portion, the hollow soil displacing tool being provided with a tubular soil displacing body received therein and having projections on its upper portion while the same soil displacing tool being also provided with slots on its inner surface for cooperation with the projections of the tubular soil displacing body, besides the apparatus being provided with a skirt axially movable along the drill column and having an outer helical ribbon surface on its upper portion.
The prior art apparatus suffers from a disadvantage of an inadequate scope of its application as regards the construction of the cast in place tubular piles because difficulties are involved in lowering the apparatus true to center into a hole previously formed by another tool and filled with a concrete mix.
Known in the art is also a method of constructing a cast in place tubular pile, which bears closely on the invention (USSR Inventor's Certificate No. 777,144), wherein a casing is driven in the subsoil, the casing being composed of a number of concentrically spaced tubular members previously capped together and having a reinforcement arranged between the tubular members.
The prior art method, however, suffers from disadvantages as listed below:
1. A low efficiency because of difficulties in driving the casing into the subsoil due to a high resistance from the subsoil.
2. The soil is inadequately compacted and over an insufficient area about the casing to insignificantly increase bearing capacity of the casing against the subsoil.
3. The surface of the casing is not protected against the corrosive action of the subsoil water thereby the casing is rapidly destroyed.
4. The proposed method does not insure that the piles will be of acceptable quality because gravel as well as the soil is likely to get into the spacing between the tubular members, since practically the spacing cannot be reduced to a satisfactory amount.
5. A limited length of the cast in place tubular piles is due to a high soil to casing resistance.
6. A high power consumption of the construction.
The invention contemplates the provision of an apparatus for constructing cast in place tubular piles and to a method of constructing such piles by the same apparatus, which make it possible to enlarge the area and amount of the soil compaction as well as to make the construction efficiency increased.